Various actuators have been used for driving lens, for example, in a digital still camera, a camcorder, a monitoring camera and the like, and in order to conduct sensing of a position of such movable lens, etc., a position detecting device is used.
For example, there are, as a device for detecting a position and a moving distance of focus lens, a device of a type using a pulse generator like a stepping motor system and a device of a type using a photosensor or a magnetic sensor for analogically detecting a moving distance in a piezo motor system. Examples of the former type are described in JP 04-9712 A, etc., and examples of the latter type are described in JP 05-45179 A, JP 2002-357762 A, JP 2006-173306 A, JP 2009-38321 A, etc.
The above-mentioned stepping motor system undergoes rotation for each of rotation angles corresponding to the number of counted pulses generated, and this stepping motor system is usually used for applications requiring long distance position detection. However, since a motor is not rotated continuously, noise during the rotation is large, which leads to generation of acoustic noise when taking a dynamic picture image, and moreover, there is a defect such as a delayed response.
For example, in a digital still camera, stepping motor systems have been mainly used so far. However, in order to place much importance on prevention of generation of acoustic noise when taking a dynamic picture image, increase in a speed of autofocus and down-sizing of an apparatus using a stepping motor system, recently piezo motor systems have been used, and for position detection by piezo motor systems, photosensors and magnetic sensors are used.
FIGS. 15A and 15B show a position detecting device with a reflection type photosensor which has been usually used so far. As shown in FIG. 15A, a reflection type photosensor 1 is configured such that a light emitting element 3 is disposed on one concave portion and a light receiving element 4 is disposed on another concave portion and the both portions are separated by a light-shielding wall 2. Also, as shown in FIG. 15B, a reflection plate 5 is provided at the side of a light emitting/light receiving surface SL of the photosensor 1 so as to be in parallel with the light emitting/light receiving surface SL and move in a direction of a line connecting the light emitting element 3 and the light receiving element 4. According to the configuration as mentioned above, light from the light emitting element 3 is reflected on the reflection plate 5 and is input into the light receiving element 4, and the position and the moving distance of the reflection plate 5 (a moving body to which the reflection plate is attached) are detected by the amount of received light.
In the position detection using such a reflection type photosensor, example of a technique for improving performance of position detection and moving distance detection is described in JP 2006-173306 A, and example of improvement in linearity of an output signal is described in JP 2009-38321 A.